Automatic register for echo pulses from a plurality of objects



Aug. 9, E949. A. M. SKELLETT AUTOMATIC REGISTER FOR ECHO PULSES FROM A PLURALITY OF OBJECTS Original Filed Oct. 9, 1943 4 Sheets-Sheet 1 ATTRNEV A. M. SKEL.

Aug. w49.

LETT C REGISTER FOR ECHO PULSES A PLURALITY-OF OBJECTS AUTOMATI FROM 43 Original File'd Oct. S, 19

4 Sheets-Sheet 2 A from/EV All@ 9, 1949. A. M. SKELLETT 2,47%679 AUTOMATIC REGISTER FOR ECHO PULSES FROM A PLURALITY OF OBJECTS Original Filed Oct. 9. 1943 4 Sheets-Sheet 5 ATTORNEY 9 94 A. MSKELLETT 2,4?

AUTOMATIC REGISTER FOR ECHO PULSES FROM A PLURALITY OF OBJECTS AT TOR/VE Parenred Aug. 9, 1e

AUTOMATIC REGISTER FOR ECHO PULSES FROM A PLURALITY OF OBJECTS Albert M. Skellett, Madison, N. J.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Original application October 9, 1943, Serial No. 505,673, now Patent No. 2,426,245, dated August 26, 1947. Divided and this application November 8, 1945, Serial No. 627,492

This application is a division of my copending application Serial No. 505,673, iiled October 9, 1943, Patent No. 2,426,245, August 26, 1947, assigned to the same assignee as the present application. The invention claimed herein relates to an automatic register for indicatingon separate dials the ranges of two or more objects without the necessity of employing a manual range gate. An illustrative embodiment of the invention is described herein in connection with a stroboscopic indicator such as is disclosed in the said application Serial No. 505,673. The present application also discloses a scale changing system which is claimed in my copending application Serial No. 627,491, iiled November 8, 1945, now Patent No. 2,432,453, granted December 9, 1947,

4 Claims. (Cl. 343-13) and a manual range gate which is claimed in my copending application Serial No.- 627,493, led November 8, 1945, now Patent No, 2,432,454, granted December 9, 1947, both of which applications are assigned to the same assignee as the present application.

The stroboscopic type oi' indicator is designed.

to replace the cathode-ray type of indicator commonly used in radar systems. The stroboscopic indicator is based on the stroboscopic illumination of moving or rotating scales and dials, the flashes of light being set oi by the received reflections. The range, azimuth, and elevation reaciings may appear in numerical form in Windows as if the scales on which the numbers are laid out were stationary at the correct values for the reflecting object in question. Two-dimensional iield images such as map-like representations in polar coordinates may also be provided like those produced in cathode-ray tubes but of greater brilliance and size. These may or may not employ screens in which the glow persists momentarily after illumination. Automatic switching may be provided so that the apparatus assigns reections received from a plurality of objects to diiierent windows which give simultaneous readings.

The invention has among its advantages simplicity, increased ruggedness, low voltage operation, increased accuracy.

A further advantage is .the low speed of the rotating parts, which need not exceed 1800 revolutions per minute.

An object of the invention is to reduce personal error in reading the range, azimuth or elevation of the reflecting object, particularly in the case of an unskilled observer.

As used in radar indicators the cathode-ray tube operates by moving a pencil of electrons 55 over a stationary scale, the electron beam being modulated at each sweep to give an indication at the same iixed position on the scale. Thus an apparently stationary mark is observed. The stroboscopic type of indicator operates on a reverse principle. The scale moves at high sp' ed past a xed index and the illumination of the scale is modulated so as to give a iiash of light Whenever the correct part of the scale is opposite the index. The effect upon the observer is the same in either case, namely, the appearance of a stationary mark on a stationary scale.

In measuring range by reflected pulses it has not been found practical to use a scale rotating in syhchronism with the outgoing pulses and making one revolution per pulse. The reasons for this are, iirst, that the speed required of the rotating scale is too high, and second, that it is not possible to synchronize a rotating scale 4with the outgoing pulses in some radar systems because the pulses are not emitted at a uniform time rate.

In accordance with the invention, low sed scales may be used and a considerable amount of jitter or irregular spacing of the outgoing pulses may be tolerated.

For the azimuth or elevation scales it is entirely practical to synchronize the scales with the motion of the antenna. At the relatively slow speeds of the azimuth and elevation scales the flicker of the ashes may loe-observable in some cases but this will present no serious diiilculty since the overall effect is that of a stationary dial or scale illuminated with intermittent rather than steady light. l

In the drawings,

Fig. 1 is an elevational view of the indicator panel in a one-dimensional indicating system embodying the invention;

Figs. 2 and 3 constitute a schematic diagram of the electrical and mechanical apparatus associated with the panel of Fig. 1, when these iigures are arranged as in Fig. 4;

Figs. 5 and 6, when arranged as shown in'Fig.

7, .constitute a schematic diagram of an automatic register system for exhibiting the ranges of two or more objects simultaneously on separate dials; and

Fig. 8 is an elevational view ofthe dials associated with the system of Figs. Sand 6.

One-dimensional indicating system One embodiment illustrative of the invention is shown in Figs. i to 4, inclusive. This embodiment is restricted to measurement of a single dimension, namely, the range. In a class A representation, horizontal extensions indicate range or distance and a vertical line or mark indicates the location of an object at a distance shown by the horizontal position of the line or mark. Provision is made to display a class A representation of the ranges of several distant objects simultaneously against a calibrated scale from which the approximate range of each object may be read directly, for example in yards. There is also provided a single range dial from which may be obtained a more accurate reading of the range of any desired one of the distant objects. A manual range gate is provided and associated with a movable marker in the class A indicator so that a particular object, the range of which it is desired to register on the range dial, may be readily selected. The object selected may be changed for another whenever desired by repeat- .ed manipulation of the range gate. An expanded scale is provided whereby the precision of the range measurement indicated by the range dial may be increased by a predetermined factor when desired, a factor of ten being preferred. The range dial and the 'class A range indicator comprise rotating elements each of which is stroboscopically illuminated only at those instants when it presents a correct range reading.

Fig. 1 shows the external appearance of the device as it may be arranged for the convenience of an operator. A portion of the indicator panel is shown at and is provided with windows |0| and |02 which may have suitable frames or bezels. Behind the window |0| is mounted a range dial comprising a drum |03, preferably translucent, upon which are placed indications such as a numerical scale of ranges. Provision is made for rotating the dial |03 and illuminating it stroboscopically when a correct range indication appears within the window |0| at a stationary index |04 that may -be placed vbefore the dial |03 to fix the exact point of reading. Behind the window |02 is provided a rotating drum |05 with a helical mark which is made to appear, when stroboscopicaily illuminated, as a vertical or nearly vertical line segment showing through the window. A stationary scale |06 is provided for reading the position of the line segment when illuminated. |The drum |05 may be illuminated a number of times during each revolution to produce a plurality of lines such as are shown at |01, |08 and |09 to indicate the ranges of objects at different distances. The drum |05 may also be illuminated once per revolution to produce an arbitrarily movable line ||0, which may be distinguished from the lines |01 to |09, inclusive, in any suitable way as for example by a different color of illumination, may lbe provided under manual control of a knob to aid in selecting one of the distant objects the range of which is to be indicated more precisely by the reading of the dial |03. Another knob ||2 may be provided to control an expanded scale and the associated indication of a separate dial ||3 mounted next to the dial |03 and appearing within the window |0|. The dial ||3 is stationary except when ro- -tated manually by means of the knob |2 and is illuminated together with the dial |03 by the stroboscopic light source. The mechanism associated with the panel |00 will be described hereinafter with reference to Figs. 2, 3 and 4.

The manner in which the system is manipulated by the operator may be described with reference to Fig. 1, it being assumed that the internal mechanism is operating and has been 4 properly adjusted. First, it will be appreciated that the external appearance of any stroboscopically illuminated device will generally differ from the external appearance of the same device when viewed in ordinary illumination. The windows |0| and |02 are assumed to be viewed with the dial |03 and the drum |05 revolving and stroboscopically illuminated. The operator sees in the window |02 the marks or lines |01 to Ill, inclusive, as shown in Fig. l. The dial |03 would appear blurred and unreadable unless the movable range mark ||0 were placed in coincidence with one of the lines |01 to |09, inclusive and the knob ||2 were properly set as explained hereinafter. In using the system, the operator, observing the lines |01 to |09, inclusive, decides which one of the objects represented 4by these lines is of special interest and he turns the knob to move the mark ||0 to coincide with the desired line and adjusts thte knob ||2 properly as explained hereinafter. The dials |03 and ||3 are then strobosc-opically illuminated to show the range of the selected object legibly and apparently stationary opposite -the index |04. Another object may be thereafter selected by turning the knob to bring the mark ||0 in coincidence with the second. selected line and by readjusting the knob ||2 if need be, when the stroboscopic illumination of thel dials |03 and ||3 will change ,to display the range of the second object. Within the windt y |0| in Fig. 1, an illustrative range reading is shown on the expanded scale, indicating an object at a range of 83,500 yards. This reading could be observed by bringing the mark,

I|0 to coincide with the line |09 as shown. To dispense with the expanded scale and use what is commonly called the main scale, the knob ||2 may be turned until a numerical 0 appears on the dial ||3 and a step further -to operate a switching mechanism which may be mechanically coupled to the knob |2 to switch over the electric circuit from a condition termed the expanded scale condition to one termed the main scale condition as hereinafter described.

Figs. 2 and 3 show the mechanism and circuits behind and associated with the panel |00 of thev device shown in Fig. 1.

In Fig. 2 a pulsing circuit 200 is shown connected both to an oscillator 20|, preferably of ultra-high frequency, and a square wave generator tube 202 which with connected elements will be referred to as the start-stop circuit. The oscillator 20| is connected to a suitable radiating system such as a dipole antenna 203 mounted at the focus of a paraboloidal projector 204. The output of the start-stop circuit is connected to the grid circuit of a vacuum tube 205 in the anode circuit of which is connected a. timing resistor 206 and condenser 201. The condenser 201 is also connected in the input circuit of a square wave generator tube 208, which serves as a narrow automatic range gate. For the reception of electromagnetic waves there may be provided a directionally selective receiving system comprising a dipole antenna 209 mounted at the focus of a paraboloidal reflector 2|0. The antenna 200 is connected to the input of a radio receiver 2| the output of which is combined with the output of the tube 208 in the input circuit of amplifying tube 2 2.

In Fig. 3 suitable power terminals 300 are shown connected to a motor 30| to the shaft of which are keyed the dial |03, the drum |05 and a pair of rotary switches or commutators 302 and 303. The commutator 302 is connected with a source 304 o! direct current and a timing resistor 305 and either one of two condensers 306 and 301.

The dial |03 may be translucent and may have The broad principle of operation and the salient features of the structure of Figs. 1 to 3, inclusive, will first be briefly given before presenting a more detailed description. The power supplied to the terminals 300 may be conveniently in the form of 60-cycle alternating current to drive a common type of motor at a speed of approximately 1800 revolutions per minute, that is about thirty revolutions per second. This particular speed is not essential but has been found both suitable and convenient. The motor 30| drives the dial |03, the drum and the commutators 302 and 303 directly at this speed. At a preferably more rapid rate, say 200 to 1,000 or more times per second, the pulsing circuit 200 briefly energlzes the radio transmitter 20| to deliver a short train of waves to the'antenna 203, which train is projected as a pulse of electromagnetic waves from the projector 200. Simultaneously with the energization of the radio transmitter, the pulsing circuit energizes the tube 202 to generate a square-topped pulse used to block the tube 205 and start a charging current in the resistor 200 and condenser 201. The tube 205 and associated timing elements will be hereinafter referred to as the fast timing circuit. The time constant of the circuit is preferably so predesigned that the potential of the condenser 207 will pass through a suitable range of values at a substantially linear time rate during the brief time required for an electromagnetic pulse to travel from the project 200 to the most distant object the range of which is to be measured and to return to the reflector 2|0. The commutator 302 is arranged to connect the battery 500 to the other timing circuit comprising the resistor 305 and the condenser 306 to charge the condenser 30S at a rate relatively slow compared with the condenser 207 to cover a similar suitable range of potentials on the condenser 300 during a single revolution of the commutator. This latter timing circuit will hereinafter be referred to as-the slow timing circuit. Due to the relatively slow rate of revolution of the mechanical system, it

is permissible to facilitate the description by assuming for the time being that the dial |03 and drum |05 remain stationary during the time between two pulses of the pulsing circuit 200. It is also permissible at this point in the description to assume that the potential of the condenser 306 remains constant during the interval between two pulses. Provision is made to compare the potential of the condenser 306 and the potential of the condenser 201 in the grid-cathode circuit of the tube 208. At some instant during the period between successive pulses the potentials of the condensers 306 and 207 will be of the proper relation to each other to unblock the tube 208 and thereby initiate a square-topped pulse therein. The circuit of the tube 200 is preferably sodesigned that the square-topped pulse produced is one of relatively short duration. The tube 208, however, does not directly connect with the flash lamps but merely energizes or sensitizes 0 the input circuit of the amplifying tube 2 l2. The tube 2|2 will operate to flash the lamps 300 and 3|0 only if a reilected pulse is received by the radio receiver 2li during one of the brief intervals when the tube 2|2 is sensitized.` The scale on the dial |03 is so calibrated that when the lamp 308 iiashes the correct range of the distant object from which the reflected pulse was received is shown within the window |0| opposite the stationary index |04. The stationary scale |00 adjacent the frame |02 is so calibrated also that when the lamp 3|0 ashes the portion of the slot 309 which is illuminated and shows through the window |02 is opposite the same range reading on the scale |00 as is simultaneously appearing on the dial |00.

The illumination of the lamp 308 is preferably further restricted under the control of the manual range gate so that the dial |03 will not be illuminated unless the range of the distant object and the setting of the manual range gate agree. The lamp 0|0 on the other hand is preferably not under the control of the range gate so that it may flash whenever the range of a distant object agrees with the position of the slot 300 with respect to the scale |00. The lamp 3H is l drum |00.

Returning now to the effect of the rotation of the mechanical systems, the shaft and attachments will nolonger be considered as standing still. During each interval between pulses the dial |03, drum |05 and lthe commutators 302 and 303 will have moved a small fraction of a revolution and the potential o'f the condenser 306 will have increased accordingly. The dial l 00 and the drum |05 have advanced to a slightly `higher range reading. The critical relation of potentials of the condensers 20| and 306 now occurs-at a slightly later epoch with respect to the start of the outgoing pulse from the projector 200. As a result the tube 200 will energize the tube 2|2 at a correspondingly later epoch and the lamps 300 and 3|0 will flash only in response to an incoming reflected pulse from a somewhat more distant object, the range of which corresponds to the new reading of the dial |03 and drum |05.Accordingly, in each succeeding cycle of the pulsing circuit 200 the lamp control circuits will be energized at the particular epoch which corresponds to the range reading simultaneously presented at the windows by the dial `|00 and the drum |05. During each revolution of the mechanical system the lamp control circuits will have been brielly energized ,successively at a succession of range readings distributed over the total range of the apparatus. When the range lreading correspondsv to the range of an object the reflected pulses from that object will be enabled to flash the lamps 'at least once during the revolution. As the speed of rotation is suiilcient to provide 30 ilashes per second a substantially flickerless scale reading is obtained.

In order that no pulses be lost due to being returned from objects having ranges that lie between the successive range readings for which the lampcontrol circuits are energized, the automatic range gate should be open each time for a. sufcient interval to admit all returning pulses froml objects in a zone of a certain width. The

range gate should have a width of about 11/2 per cent of the maximum range, or 1500 yards in 100,000 yards. For an expanded scale of ten times the sensitivity of the main scale, the range gate width in this example may be reduced to one-tenth or 150 yards. The actual readings may be more accurate than the -frequency ratio indicates, due to the fact that unless the frequencies are exactly commensurate succeeding readings on the same range will vary slightly and the eye will naturally read the average of the values presented by the scale.

The lamp 3I0 will flash once perrevolution for each received pulse and when several pulses are received from objects at different ranges the lamp 3I0 will flash when the slot 309 is opposite each of a number of different readings on the scale |06 producing a plurality of lines such as I01 to |09, inclusive. The commutator 303 will flash the argon lamp 3.|I once for every revolution of the drum |05 at a particular angular position which maybe controlled by means of the knob I I I to produce an arbitrarily movable mark IIO of a different color from the lines |01 to |09, inclusive. By moving the mark IIO to coincide with one of the lines such as |01 to I09,

inclusive, the lamp 308, will be made to flash to show a precise reading of the range corresponding to the particular line selected by the operator.

The purpose of the expanded scale is to cover a restricted group of ranges with a. more precise balance of voltages in the input of the tube 208 as well as with a narrower range gate. The particular portion of the scale |06 to be covered by the expanded Scale is indicated by the dial ||3 which places an additional digit in front of the reading of the scale |03 by means of a mechanism which will be more fully described hereinafter.

The circuits shown in Fig. 2 will now be described in somewhat greater detail.

Start-stop circuit The start-stop tube 202 may contain, in a single envelope, if desired, two triodes 2I3 and 2|4, the triode 2I3 including a cathode 2|5, a grid 2I6, and an anode 2I1 and the triode 2I4 including a cathode 218, a grid 2I9 and an anode 220. A supply source 22|, such as a battery, may have its negative terminal grounded as at 222. The positive terminal of the source 22| may be connected to the anode 2I1 through an anode load resistor 223 as well as directly to the anode 220 and through a grid load resistor 224 to the grid 2I9. The cathodes 2|5 and 2I8 may be conncctedvto ground through cathode resistors 225 and 226. The pulsing circuit 200 may be connected to the grid 2I6 by a blocking condenser 221. A grid resistor 220 is preferably connected between the grid 2I6 and the common terminal of the cathode resistors 225 and 220. A coupling condenser 229 is provided between the anode 2I1 and the grid 2I9.

In the operation of the start-stop circuit, the

triode 2I4 is normally conducting because of the connection of the grid 2I9 with the positive terminal of the supply source 22| through the resistor 224. The anode-cathode current of the triode 2I4 flowing through the properly proportioned resistor 225 provides a blocking potential upon the grid 2| E which renders the triode 2I3 normally non-conducting. The connection of the grid 2|9 to the positive terminal of the source 22| through the resistor 224 renders the grid potential positive with the result that-grid current flows through the triode 2I4 and adds to the biasing current in the resistor 225. The triode 2I3 has substantially the full supply voltage impressed across between'its anode and cathode although, as aforementioned, anode current is blocked by the negative potential impressed upon the grid 2I6 by the current flowingv in the resistor 225. This condition of the start-stop circuit is a stable one but it may be disturbed by the receipt of a pulse from the circuit 200.

The pulsing circuit 200 is preferably arranged to impress a, pulse upon the grid resistor 220 through the blocking condenser 221, the pulse being of such polarity as to render the grid 2I8 more positive with respect to the cathode 2|5. The pulse is preferably of sufficient strength to overcome the negative bias impressed upon the grid 2I6 by the resistor 225, thereby rendering the triode 2I3 conductive. The flow of current from the source 22| through the resistor 223 and the anode-cathode circuit of the triode 2I3 pro- `duces a drop in the potential of the anode 2I1.

As a result, the charged condenser 229 begins to discharge through the resistor 224 and at the same time the condenser 229 effectively places a negative bias upon the grid 2I9, thereby causing the triode 2I4 to cut off' its own anode-cathode current. The cessation of the current in the triode 2 I4 removes some of the negative bias from the grid 2I6 and enables the supply source 22| to maintain the anode-cathode current in the triode 2I3 even though meanwhile the activating pulse'from the circuit 200 may have ceased. The condenser 229 continues to discharge through the resistor 224 and when sufficiently discharged, the triode 2I4 again becomes conductive and its anode-cathode current restores the negative bias in the resistor 225 to cut off the'anode-cathode current in the triode 2|3, thereby returning the start-stop circuit to the original stable condition. The time required for the cycle of operations in the start-stop circuit is determined mainly by the capacitance of the condenser 229 and the resistance of the resistor 224. The cycle may be repeated by supplying successive pulses to the grid 2 I6 from the pulsing circuit 200. The start-stop circuit develops a good square-topped wave between the cathodes 2|5 and 2I8 and the ground 222 which wave may be impressed upon the grid of the trigger tube 205 by means of a blocking condenser 230 and a. grid resistor 200.

Fast timing circuit The fast timing circuit comprises the vacuum tube 205, the resistor 206 and the condenser 201. The tube may be a pentode having a cathode 23|l a control grid 232, a screen grid 233, a suppressor grid 234 connected -to the cathode, and an anode 235. The cathode 23| may be grounded and the anode 235 may be connected to the positive terminal of the source 22| through the resistor 206.

In the operation of the fast timing circuit, the grid 232 normally maintains the tube 205 in a conducting condition due to the potential drop across the resistors 225 and 226 being balanced with respect to the grid 232 by a charge on the condenser 230. When the potential across the resistors 225 and 226 falls during the operation of the start-stop circuit, this drop in potential transmitted through the condenser 230 impresses a negative potential 'upon the grid 232, thereby blocking the tube 205 and permitting charging current to ow to the condenser 201 through the resistor 206. At the end of the square-topped pulse when the potential difference across the resistors 225 and 226 is restored, the grid 232 returns to substantially ground potential, rendering the tube 205 conducting and permitting rapid discharge of the condenser 201 through the tube 205.

Automatic range gate The automatic range gate comprises the square wave generator 206 and associated circuits. The tube 208 may contain, in a single envelope, if desired, two triodes 236 and 231, the triode 236 including a cathode 238, an anode 240 and the triode 231 including a cathode a control grid 202 and an anode 243. The cathode 24| may be directly grounded and the cathode 238 may be connected `to ground through a coupling condenser 206. The anodes 240 and 263 may be connected to the positive terminal of the source 22| through anode circuit resistors 236 and 206, respectively. The anodes 230 and 203 may be cross-connected to the grids 262 and 235, respectively by coupling condensers 241 and 233. The grid 239 may be connected to the positive terminal of the condenser 201 through a coupling :resistor 209. The grid 202 may be connected to ground through either one of two resistors 250 and 25| under the control of a switch 252.

In the operation of the automatic range gate, the potential of the condenser 201 is continuously compared with the potential of a selected one of the condensers 306 and 301 in the grid-cathode circuit of the triode 236. The potential of the condenser 201 acts by virtue of direct connection in the grid-cathode circuit, while the potential of condenser 306 or 301 is impressed upon the cathode'236. The potential of the cathode 238 a control grid 239 and.

is thus changing at a slow rate and the potential of the grid 230 is changing at the fast rate. At the start of each fast cycle the grid potential is more negative with respect to that of the cathode 233 than the cut-ofi:` voltage of the triode and as it rises this cut-ofi' potential is reached and the Atriode l236 starts to conduct. Before this critical potential relation is reached the triode 331 is conducting due to the grid 262 being connected to the cathode 24| through one of the resistors 250 and 25|, and the coupling condenser 261 contains a charge of substantially the full voltage of the source 22|. When the triode 236 becomes conducting, its anode potential falls due to the iow of current in the resistor 245, and this potential drop is impressed on grid 262 through condenser 201, thereby immediately blocking the .triode 231. The condenser 241 rapidly discharges through the resistor 250 or 25|, removing after a definite interval the blocking potential from the grid 252 and permitting current to flow again. lit will be noted that while the triode 231 was blocked, the coupling condenser 208 was being charged through vthe resistor 246, 243 and the condenser 201. When the triode 231 has resumed conductivity, the charge-on the condenser 248 is eiectively thrown across between the grid 239 and the cathode 236 to form a blocking potential to aid in restoring the triode 236 to the normal condition. The generator 208 thus produces a square-topped pulse preferably of brief duration which is impressed upon the input circuit of the flashing tube 2|2. During the normal blocked condition of the triode 236, the triode 231 is coriductive and hence the anode 243 may be arranged to be very little above the potential of the cathode 20|. During the brief period of blocking in the triode 231, the anode 243 assumes substantially the full battery potential. The potential variation of the anode 243 `thus constitutes a narrow square-topped Wave of potential. The duration of the narrow pulse may be varied by means of the switch 252 to select one of the other of the resistors 250 and 25| through which to discharge the condenser 241.

Flashing circuit The flashing circuit comprises the tube 2|2 and associated elements. The square-topped wave from the generator 206 is impressed upon the flashing circuit through a coupling condenser 253. The ashing tube 2|2 may contain, in a single envelope, if desired, two triodes 254 and 255, the triode 250 including a cathode 256, a grid 251 and an anode 256 and the triode 255 including a cathode 259, a grid 260 and an anode 25|. The ungrounded side of the radio receiver 2li may be connected to the grid 251 through a coupling condenser 262 and the output of the automatic range gate may be connected into the gridcathode circuit of the triode 254 by means of the coupling condenser 253. The tube 2|2comprises two stages of amplification. Normally the grid 251 is biased more negative than its cut-oil? potential so that echoes from the radio receiver cannot get through to operate the dashing lamps 308 and 3|0. When the range gate is impressed on this grid it brings its potential to cut-01T and the echoes, which are of positive potential can then get through to triode 255 Where they are' amplified for use in triggering on" the flash tubes 308 and 3H).v Thus the tube 2 i2 is operated when a signal is received by the radio receiver 2| i provided at the same time the triode 250 is unblocked by the action of the tube 208.

Flash lamps The ash lamps 308, 3|0 and 3|! are preferably of the three-electrode cold type. VThe tubes 308, 3|0 and 3H have anodes 3|2, 3|3 and 3M, respectively, all of which are permanently connected across a condenser 266 and a series inductance 268 through a lead 3|5 and through the lead 3|5 and a resistor 261 to a junction point 264 in a potentiometer Aacross the source 22|. The tube 300 has a pair of control electrodes 316 and 3|1 and the tubes 3|0 and 3| have corresponding pairs of control electrodes 3|8,3|9 and 320, 32|. Ground connection is supplied over a lead 322 in a permanent connection to the control electrode 3|8 of the tube 3|0 so that this tube will flash whenever an exciting potential is impressed upon its second control Ground connection i-s supplied to electrodes 3|6 and 320 of the tubes 308 and 3| l, respectively, through a lead 323, a brush 324, a conductive band 325 of the commutator 303, a brush 326 to ground at 321 only during the passage of the brush 324 over the projection 326 of the band 325. At all other times the brush 320 connects the electrodes 3|| and 320 through another brush 349 to a disabling positive potential electrode 3 9. the control such as is supplied by a battery 350. The second control electrodes 3|1 and 3|9 of the tubes 306 and 3|0, respectively, are connected through a lead 329 to a junction point 265 in the output circuit of the flashing tube 2|2. These tubes 308 and 3|0 receive over the lead 329 a flashing voltage upon receipt of a reilected radio wave by the system at a time when the automatic range gate is open. The control electrode 32| of the tube 3| is permanently connected to the positiveterminal of a source 330 illustrated as a battery. The battery 330 becomes effective to flash the tube 3|| whenever the ground connection is apyplied to the other control electrode 320 by the commutator 303.

In the operation of the tubes 308, 3|0 and 3|| it will be evident from the foregoing description of the connections that the tube 3| i will be operated once during each revolution of the commutator 303 when the brush 321| crosses the projecting segment 320, The tube 308 will ilash provided a radio impulse is received while the automatic range gate and the manual range gate are both set for substantially the correct range. The tube 3|0 will operate independently of the manual range gate whenever a radio impulse is received during the open condition of the automatic range gate. Each flash of the lamps discharges the condenser 266 which is then recharged at a denite rate through the resistor 261 and the inductor 260 in time for the next flash.

Slow timing circuit brush 335 and then through a lead 33s, to one of the condensers 306 and 301 and then through a lead 331 and a iiexible lead 33B to step 8 of the potentiometer 33| and thence to ground. The commutator 302 comprises two conductive bands 339 and 340. The brush 334 runs continually on the band 340 and a brush 34| on the band 339.

The bru-sh 335 runs upon the band 340 except during a certain portion of each revolution when the brush 335 rests upon a projection 342 which is an integral part of the band 339. While the brush 335 rests upon the projection 342, the condenser 306 or 301 is short-circuited. When, during the revolution of the commutator 302, the projection 342 moves away from the brush 335, the condenser 306 or 301 begins to charge through the resistor 305. The charging of the condenser continues at a substantially uniform rate until the projection 342 is again brought under the brush 335 when the condenser is quickly discharged and made ready for a repetition of the charging cycle. The potentiometers 33| and 332 are preferably so arranged that the effective charging voltage is the same regardless of the steps occupied by the variable contacts of the potentiometers.

Rotating mechanical system The commutators 302 and 303 are preferably keyed to the shaft of the motor 30|. The dial |03 and the drum |05 are preferably xedly attached to the shaft `by suitable means such as 12 spider structures 342 and .343, respectively. The dial I3 is preferably mounted freely on the shaft and may be geared to the knob ||2 in known manner as, for example, by means of a suitable combination of racks and plnions. The brush 324 is preferably mounted on a spider structure 344 which rides freely on the shaft and is geared to the knob lli through another suitable combination of racks and plnions. The remaining brushes are stationary and may be supported in any suitable manner The lamp 306 may be mounted inside the dial |03 and the lamps 3|0 and 3| l inside the drum |05. The necessary leads to the lamps may be introduced through the space between the dial |03v and the drum |05.

Angular displacement of the rotating parts In setting the commutators 302 and 303 and the dial |03 and drum |05 on the shaft, the following considerations should be observed as to the relative angular positions of these elements. The dial |03, in a system intended to measure ranges up to 100,000 yards will preferably have a scale reading from 0 to 100,000 occupying a major portion of the periphery of the dial. A blank segment, shown in Fig. 3 for clarity as one-sixth of the complete circle is reserved to cover the interval ofY time required for the discharge of the slow timing circuit but this interval may be shortened considerably in practice. The helical mark 309 occupies the same proportional part of a complete circumference of the drum |05 as the numerical scale occupies in the complete circumference of the dial |03. 'I'he dial |03 and drum |05 are to be set in such a relative angular position that the reading of the dial |03 against the index |04 at the window |0| is identical with the reading of the mark 309 against the scale |03 at the window |02. The angular relation between the commutator 302 and the brush 335, should then be such that when the trailing edge of the segment 362 of the commutator leaves the brush 335, the dial |03 registers zero against the index |00. The angular position of the commutator 303 on the shaft may be determined arbitrarily.

Main scale When the expanded scale is not in use, the apparatus is said to be operating on the main scale. The potentiometers 33| and 332 are each provided with ten taps or positions, numbered from 0 to 9, inclusive, which are used with the expanded scale. An additional position M is provided adjacent to the zero position for use when operating with the main scale and is directly connected electrically in the potentiometer with the adjacent position 0. Potentiometer arms 345 and 346 for the respective potentiometers 33| and 332 are provided and may be insulatingly attached to a bar 341 in the rack and pinion system operated by the knob l2. In using the main scale the knob ||2 is rotated to bring the arms 345 and 346 on to the respective M positions of the potentiometers. This operation results in a rotation of the dial H3 through zero to one position beyond zero, at which position there is no number showing at the window |0|. The switches 252 and a switch 348 controlling the selection of the condensers 306 and 301 are preferably mechanically coupled to one of the potentiometer arms 345 or 346 in such a manner that the switches 252 and 348 are both operated whenever the arm 345 passes from' the zero position to the M position or vice versa. For the main scale, the switches 252 and 348 are operated into the andere M position bringing the resistor 25| and condenser 301 into circuit for the main scale and the resistor 250 and condenser 306 for the expanded scale. In operation with the main scale, one terminal of the condenser 307 is grounded so that the potential impressed upon the condenser 266 by the slow timing circuit is simply the potential of the condenser 301. The resistor 25| is proportioned to give the desired width to the automatic range gate. The reading in the window Il is shown by the number appearing on the dial |03.

Expanded scale In operation with the expanded scale, when one of the marks such as |01, |08 and |09 ap' pearlng at the window |02 has been selected by the operator, the knob ||2 is turned to bring the first digit of the range of the selected line into view in the window |i. For example, if the line |09 is chosen (reading approximately 83,000 yards on the scale |06) the digit 8 is brought into view in the window |0|, as shown in Fig. 1. This operation moves the potentiometer arms 365 and 388 to the position 8 on the potentiometers 33| and 832, as illustrated in Fig. 3. It also operates the switches 252 and 348 to the 0-9 position, bringing into circuit the resistor 250 and the condenser 306'. The condenser 305 is now in series with a potential provided between ground and position 8 of the potentiometer 33| and this potential is added on to the potential of the condenser 308 inthe condenser 248 for comparison with the potential in the fast timing circuit. The

potential impressed upon the slow timing circuit is the same regardless of the position of the po-` tentiometers, when, as is preferable, the potential between each pair of corresponding positions on the two potentiometers is the same. The resistor 250 is preferably designed to reduce the width of the automatic range gate to one-tenth the value used with the main scale. The condenser 306 is preferably made ten times the capacity of the condenser 301 so that during the period of a single revolution the condenser 306 will acquire a potential only one-tenth as great as that attained by the condenser 307 when using the main scale. The potential difference between two adjacent positions of the potentiometers is thus spread out by means of the condenser 306 to occupy a complete cycle of the slow timing circuit. The reading in the window i 0| is comprised by the reading of the dial |03 pre- !xed by the digit exhibited by the dial H3.

In the system as illustrated, switching over to the expanded scale expands the range covered by the drum |05 and the images in the long window |02. The scale |06 will then represent hundreds of yards instead of thousands as for the m'ain scale and as the knob ||2 is turned the portionI of the total range covered by the scale |02:` will be moved along the total range along with the indication of the dial H3.

Automatic register for two or more objects under observation associated with a transmitting reflector 103. The

pulsing circuit '|00 is also connected to a timing gil system comprising a start-stop tube 704, a trigger tube 105, and an automaticv gate tube '|06 which elements and associated circuits correspond to the system of Fig. 2 comprising the tubes 202, 205 and 208. A receiving reflector 101 is provided with a receiving antenna |08 connected to a radio receiver'l09. The output of the radio receiver is connected to a tube 'H0 arranged like the flashing tube 2|2 in the system of Fig. 2 but which in this case does not directly flash the lamps but controls intermediate apparatus for this function.

The output of the tube H0 is connected to the input of a tube in the output of which is a rectifier 'H2 connected back through a lead 'H8 to the grid circuit of the left-hand triode in tube H0. The output of the tube 'H0 is also connected, by a lead |22 to the input of a flashing tube 'H8 which is in turn connected to a flash lamp 1| 5 arranged in position to illuminate a rotatable dial '1| 6. The dial H6 is one of three shown mounted side by side. behind separate windows in Fig. 8.

The tubes H0, 'lll and 'H0 and their asso.- ciated circuits, together with the flash lamp 'H5 and the scale H6 constitute one of a plurality of registry channels. .Another such channel is shown in Fig.-6v comprising tubes 800, 80|' and 808, a flash lamp 005 and a scale 806. The scale 805 and a third scale 808 are shown alongside the scale l I6 in Fig. 8. Additional registry channels may be connected according to the scheme shown but for the sake of clarity in the drawings, only three scales are shown and two registry channels.

The internal connections in the channel shown in Fig. 6 are the same as in the first registry channel, Fig. 5, except that a connection like the lead 722 in Fig. 5 is omitted in Fig. 6 and instead a the cathode circuit of the tube 1li ond channel with the third channel, not shown, in the same way that the lead lll interconnects the first and second channels.

The automatic gate tube 106 is connected by a lead 7|0 with the input circuit of each flashing which the two shown are 'Ht and 800, a branch lead 'l 0 going to the tube 'l Il and a branch 807 going to the tube 804.

The output ofthe radio nected directly to the input of the tube 'H0 and also through a lead 720 with the input of the tube 800 and other tubes of similar function to tube 000, not shown.

In the operation of the system of Figs. 5 to 8, inclusive, the radio transmitting system and the tubes 708, '|05 and '|06 operate the same as the radio transmitting system and the tubes 202, 205 and 208, respectively in Fig. 2. The output of the radio receiver 709 is impressed upon the tubes "H0, 800 and others of similar function each associated with one of the dials l 6, 806, 808, etc. The tube 'H0 serves as a two-stage amplifier and will respond to amplify the first pulse which is received. The tube lli is actuated by the pulse in receiver 709 is conthe tube 1 i0 to initiate 'a square wave which serves the interval between pulses of the circuit 100 so that the amplifier 1I0 may be ready to receive a succeeding reflection from the same object. The blanking feature greatly reduces noise interference besides limiting the amplifier to reflections from a single object. It will be evident that as soon as a reflection passes through the amplifier 1&0 the blanking circuit takes control and excludes reflections from other objects at the same time cutting out random peaks due to noise.

The circuit of the tube 'llt differs from that of the tube Still and following tubes of similar function in having the lead 722 coupling the cathode circuits of the two portions. In the tube 800 the lead '122 is omitted and the cathode of the second half of the tube is connected through the lead l il to the cathode circuit of the tube lll i. When the tube 'il l is operating due to the first channel registering a reflection, the point 'E23 in the cathode circuit of the tube lli, at which point the lead lil is connected will be at a more negative potential than when the tube i ii is not operating.A The potential of the point itil is transferred to the right-hand cathode dil@ of the tube 3mi by the lead lll, thereby bringing this cathode to an operating potential whenever the tube 'lll ls operating. When the tube lil is not operating, the cathode 809 is at a non-operating potential, i. e., it ls so positive with respect to its control grid that no velectrons flow from it.

The lead mit performs a function similar to that of the lead lil. Thus the right-hand oathode of the first tube in any channel, except the first channel, is biased beyond cut-off unless the preceding channel is operating on a reflection.

The ilrst reflection received will find only the first channel operative and will take over the tube 'H0 and register on dial HS in the first window. The mechanism of this response is by way of the connection of the output circuit of HG to the input circuit of the tube l i d, permitting the flashing circuit of the tube 'lill to be energized and the tube 1 I 5 flashed when the dial 'H6 shows the correct reading for the first reflection. The next reflection to come in finds the tube lili inoperative due to the blanking pulse from the rectifier H2 but is able to operate the tube 800. Operation of the tube 800 initiates a pulse in the tube 80| thereby placing a blanking pulse upon the tube 80G through the lead 802 and an enabling pulse on the following tube through the lead 803. The tube 800 also energizes the flashing tube 8M to flash the lamp 805 at the proper instant when the scale 806 indicates the correct range of the object from which the second reflection is received.

A third reflection finds tubes 1li) and 800 both disabled by blanking pulses but is able to operate the third flashing circuit to give a reading on the dial 808. Other channels that may be added to the chain operate in similar manner. When a second reflection from the first object is received, the blanking pulse on the tube l l will have ended and that tube will be ready to transmit an impulse to the flashing tube 'l I4 as before.

What is claimed is:

1. A system for separately registering echo pulses received from a plurality of objects at different distances in response to exploring pulses projected at equal time intervals, comprising a succession of registry channels, a common input circuit therefor, individual output circuits therev for, indicating means individual to the respective output circuits of the said registry channels. individual blanking circuits connected to the respective output circuits of the said registry channels, the first of said registry channels being initially operative and the succeeding registry channels being initially inoperative, each blanking circuit being actuable by an echo pulse passing through the connected registry channel to impress a blanking potential upon said registry channel for a time interval of slightly less duration than the interval between successive projected exploring pulses to render said registry channel inoperative during said interval, and, in the case of all but the last registry channel, to impress an energizing potential upon the next succeeding registry channel to render said next registry channel operative.

2. A system for separately registering echo pulses received from a plurality of objects at different distances in response to exploring pulses projected at equal time intervals, comprising a succession of registry channels, a common input circuit therefor, individual output circuits therefor, indicating means individual to the respective output circuits of the said registry channels, individual square Waveegenerators connected to the respective output circuits of the said registry channels, the first of said registry channels being initially operative and the succeeding registry channels being initially inoperative, each square wave generator being actuable by an echo pulse passing through the registry channel connected thereto when said channel is operative to impress a square wave upon the said registry channel connected thereto for a time interval of slightly less duration than the interval between successive projected exploring pulses in the polarity required to render said registry channel inoperative, and, in the case of all but the last registry channel, to impress the said square wave upon the next registry channel in succession in the polarity required to render said next registry channel operative.

3. A system for separately registering echo pulses received from a plurality of objects al; different distances in response to exploring pulses projected at equal time intervals, comprising a V plurality of registry channels, a common input circuit and individual output circuits therefor, indicating means individual to the respective output circuits of the said registry channels, individual square Wave generators connected in the respective output circuits of the said registry channels, the first of said registry channels being initially operative and the remaining registry channels being initially inoperative, the said square wave generator individual to the first registry channel being actuable by an echo pulse passing through said channel to impress a square wave upon said first registry channel for a time interval of slightly less duration than the interval between successive projected exploring pulses in a polarity required to render said first registry channel inoperative and upon said second registry channel in the polarity required to render said second registry channel operative, the square wave generator individual to the second registry channel being actuable by an echo pulse passing through said second registry channel to impress a square wave upon said second registry channel for a time interval of slightly less duration than the interval between successive projected explor- `lng pulses in the polarity required to render said second registry channel inoperative and upon said third registry channel in the polarity required to render the third registry channel operative, and the square wave generator individual to the third registry channel being actuable by an echo pulse passing through said third registry channel to channel to render the same inoperative for an equal time interval.

4. A system for separately registering echo pulses received from a plurality of objects at different distances in response to exploring pulses projected at equal time intervals, comprising a succession of pulse ampliers. a common input circuit therefor, individual output circuits therefor, indicating means individual to the respective output circuits of the said pulse ampliers, individual blanking circuits connected to the respective output circuits of the said pulse ampliers. the rst of said pulse ampliiiers being initially operative and the succeeding pulse ampliers being initially inoperative, each blanking circuit being actuable by an echo pulse passing through l the pulse amplifier connected thereto to blank the said' pulse amplier for a time interval of 5 plier operative.

slightly less duration than the interval between successive projected exploring pulses, and, inthe case of all but the last pulse amplifier in they succession, to render the next succeeding pulse am- ALBERT M. SKELLETT.

REFERENCES CITED The following references are of record in the 10 file vof this patent:

UNITED STATES PATENTS Epstein Dec. 1'7, 1946 

